Gestalt psychology (also Gestalt theory of the Berlin School) is a theory of mind and brain that proposes that the operational principle of the brain is holistic, parallel, and analog, with self-organizing tendencies. The classic Gestalt example is a soap bubble, whose spherical shape (its Gestalt) is not defined by a rigid template, or a mathematical formula, but rather it emerges spontaneously by the
parallel action of surface tension acting at all points in the surface simultaneously. This is in contrast to the "atomistic" principle of
operation of the digital computer, where every computation is broken down into a sequence of simple steps, each of which is computed independently of the problem as a whole. The Gestalt effect refers to the form-forming capability of our senses, particularly with respect to the visual recognition of figures and whole forms instead of just a collection of simple lines and curves.

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The key properties of Gestalt systems are emergence, reification, multistability, and invariance.

Emergence is demonstrated by the perception of the Dog Picture, which depicts a Dalmatian dog sniffing the ground in the shade of overhanging trees. The dog is not recognized by first identifying its parts (feet, ears, nose, tail, etc.), and then inferring the dog from those component parts. Instead, the dog is perceived as a whole, all at once.

Multistability (or Multistable perception) is the tendency of ambiguous perceptual experiences to pop back and forth unstably between two or more alternative interpretations. This is seen for example in the Necker cube, and in Rubin's Figure / Vase illusion shown to the right.

Invariance is the property of perception whereby simple geometrical objects are recognized independent of rotation, translation, and scale, as well as several other variations such as elastic
deformations, different lighting, and different component features. For example the objects in A in the figure are all immediately recognized as the same basic shape, which are immediately distinguishable from the forms in B. They are even recognized despite perspective and elastic deformations as in C, and when depicted using different graphic elements as in D.

Emergence, reification, multistability, and invariance, are not separable modules to be modeled individually, but they are different aspects of a single unified dynamic mechanism.

Both von Ehrenfels and Edmund Husserl seem to have been inspired by Mach's work Beiträge zur Analyse der Empfindungen (Contributions to the Analysis of the Sensations, 1886), in formulating their very similar concepts of Gestalt and Figural Moment, respectively.

Early 20th century theorists, such as Kurt Koffka, Max Wertheimer, and Wolfgang Köhler (students of Carl Stumpf) saw objects as perceived within an environment according to all of their elements taken together as a global construct. This 'gestalt' or 'whole form' approach sought to isolate principles of perception; seemingly innate mental 'laws', which determined the way in which objects were perceived.

These laws took several forms, such as the grouping of similar, or proximate objects together, within this global process. Although it has been criticised for being merely descriptive, it has formed the basis of much further research into the perception of patterns and objects (ref: Carlson, Buskist & Martin, 2000) and of research into behavior, thinking, problem solving and psychopathology.

The investigations developed at the beginning of the 20th century, based on traditional scientific methodology, divided the object of study into a set of elements that could be analyzed separately with the objective of reducing the complexity of this object. Contrary to this methodology, the school of Gestalt practiced a series of theoretical and methodological principles that attempted to redefine the approach to psychological research.

The theoretical principles are the following:

Principle of Totality - The conscious experience must be considered globally (by taking into account all the physical and mental aspects of the individual simultaneously) because the nature of the mind demands that each component be considered as part of a system of dynamic relationships.

Based on the principles above the following methodological principles are defined:

Phenomenon Experimental Analysis - In relation to the Totality Principle any psychological research should take as a starting point phenomena and not be solely focused on sensory qualities.

Biotic Experiment - The School of Gestalt established a need to conduct real experiments which sharply contrasted with and opposed classic laboratory experiments. This signified experimenting in natural situations, developed in real conditions, in which it would be possible to reproduce, with higher fidelity, what would be habitual for a subject.

The most basic rule of gestalt is the law of prägnanz. This law says that we try to experience things in as good a gestalt way as possible. In this sense, "good" can mean several things, such as regular, orderly, simplistic, symmetrical, etc. The other gestalt laws are:

Law of Closure - Our mind adds missing elements to complete a figure.

Law of Similarity - Our mind groups similar elements to an entity. The similarity depends on form, color, size and brightness of the elements.

Law of Similarity

Law of Proximity - Regional or chronological closeness of elements are grouped by our mind and seen as belonging together.

Law of Symmetry - Symmetrical images are seen as belonging together regardless of their distance.

Law of Continuity - The mind continues a pattern, even after it stops.

Law of Common Fate - Elements with the same moving direction are seen as a unit.

Law of Proximity

Figure-ground minds have an innate tendency to perceive one aspect of an event as the figure or foreground and the other as the ground or the background.

Under the gestalt theory, these laws not only apply to images, but to thought processes, memories, and our understanding of time.

Examples of the Gestalt experience include the perception of an incomplete circle as a whole or a pattern of dots as a shape - the mind completes the missing pieces through extrapolation. Studies also indicate that simple elements/compositions where the meaning is directly perceived do not offer as much a challenge to the mind as complex ones and hence the latter are preferred over the former.